Method of consolidating soils



Oct.'28, 1952 w. KJELLMAN l 2,615,307

v METHOD oF CONSOLIDATING soILs Filed April 29', 1948 QM@ www Patented c't. 2.8, 1952 iS iPATENT OFFICE "2,615,3'117 1v1-minpunt"ksoNsonDATiNGiS'oiLs Walter Kjellman, Stockholm;` Sweden ammunition-lupin' 29, 1948,* seal' -Noifeaeiv .rnsweaen Mayl s, 1941 Jemima -to :'someexamples --of -application illustrated in the attached drawing, the invention being of course not limited to these examples.

Figs. 1 and 2 are vertical sections through a soil including two different embodiments of my invention represented in a'diagrammatic manner.

In Fig. 1, line l-I is the tight iirm ground, Zthe soil layer to be treated, 3 the drains and 4 a filter covering the surface of the drained soil. The drains 3 may be of any suitable construction adapted to permit water to fiow upwards to the surface of the soil. The filter 4 is covered with a tight membrane 5, the edge of which is tightened to the ground outside the lter. From a vacuum pump 6 a pipe 1 is drawn through the membrane by means of a tight connection.

By pumping, the pressure of the air and the water in the ilter and the drains is lowered by say 12.5 lbs. per sq. inch. Consequently, thanks to the atmospheric pressure acting downwards on the membrane, the drained soil starts to consolidate as if it had been loaded with a layer of gravel, weighing 12.5 lbs. per sq. inch, that is being about 18 feet thick. As the soil consolidates, its shear strength increases considerably. The rate of consolidation depends on the properties of the soil and the radius and spacing of the drains. Normally the pumping will have to go on for some weeks or months.

After the desired degree of consolidation has been reached, the pumping is stopped and the membrane removed. Now the soil swells a little, but the main part of the consolidation and the shear strength, attained by the treatment, will remain.

In cases where the permanent load is considerable, it is advisable to apply it before the pumping starts, so that it combines with the atmos- -phericfpressurein'consolidating the soil. lThe permanent load-for *instance vvay road embank- "ment-may be 4placed `vupon the membrane for,

preferably, between they lter yand the' membrane. "The new .method A'can y"be used .inv 'soils of lclay,

silt, mud,.'peat, etc.`in 4the construction-fof streets, roads, l'q'uays and airfelds, and also when digging c'anals'and shafts. The purpose'is firstly Vto.pi'e tver'l't"learth -slides and ground ruptures by increasing the 'bearing-'capacity fof the soil, Aand ksecondly `v:to render "the settlements 'harmless' by `for'c'ingfthem -to y'-'co'rnpletion," before the concreteconstructionslaremade.

Usedias a temporary-surcharge;the atmospheriic pressure:isnormallycheaper and more effective ythan the thickestgravellayer that is practicable. Furthermore, thanks toits l'nature-Tit cannot' cause earth slides 'or'=ground ruptures,l as a thick gravel layer might do under certain conditions.

The membrane can be produced on the site by pouring a thin layer of warm asphalt from a tank car furnished with a spreader, or by spray painting, or by puddling a layer of clay, or by letting a clay suspension sedimentate. Occasionally a layer of ice or frost may serve as a membrane. Normally, however, the best way will be to make the membrane from long strips of sheet-metal, sheet-rubber or sheet-plastic or else of impregnated cloth, paper or cardboard. The strips may be delivered from the factory to the site rolled on drums. They may be joined together by gluing, welding, soldering, folding etc. or perhaps simply by overlapping and loading with sand. According to investigations already made a good and cheap membrane is produced by electrically welding together strips of sheetplastic (polyvinyl chloride) having a thickness of about 0.01 inch.

The filter 4 may consist of a layer of sand, gravel or shingle or a combination of such layers. Also a layer of twigs, straw etc., or mats made from such materials may be used. The capacity of the filter to let through Water can be increased by means of pipes of sheet-metal, wood or brick.

If the ground contains a layer of sand or gravel, penetrated or reached by the drains, the pump can suck from this layer, and then the lter may be omitted. A still greater effect can be attained by using a deep-well pump working on the level of the layer. If the layer bears much water, it is necessary anyway to prevent this water from entering the drains.

The novel method can bevused also in soils with such a permeability that neither filter nor moves extremely slowly only. The extended por-v tions of the membrane may beloaded by a line of gravel or the like to secure tight engagement with the surface of the ground. If on the vother,

hand the soil is coarse-pored, the membrane must either be extended downwards on the slope oa ditch to the rm ground, or else be tightened to a sheet-piling driven to the rm ground.

In practice the soil.; normally consists, as shown in Fig. 2, of an upper thin coarse-pored -layer 8-a dry crust withv cracks-and a -lower thick fine-pored layer e. lThen a ditch Hl may .be dug through the upper layer, and the membrane 5 is extended down into the ditch, where extending the membrane 5 up to the crest or this dam. The .water i3 above the membrane 5 is valuable also as a load acting on the drained soil. The same structure may be used at the right-hand end (not shown) of the soil to be treated.

What I claim is:

l. A drainage system for removing water from subterranean soil levels inclding a lter covering the entire surface of the soil to be treated, an air tight membrane covering said filter, a plurality of vertical drains disposed beneath said filter and communicating therewith, and a pump communicating through said membrane with said l Y l'asj to allow water to ow upwardf'to thefisurface 'of the soil and reduce the pressure on the lower side of the membrane below atmospheric pressure to consolidate the soil. I 2. The method of consolidating soils consisting in forming substantially vertical drains in the soil, covering thehvertical drains and the entire surface of the soil to be treated with a layer of lter material pervious to water, covering said filter layer with a membrane layer of air tight material, and communicating the lter material -wth a pump for reducing the pressure on the .lower side offthe membrane layerlbelow atmospheric pressure.

Numberl v Name, :Date

2,136,151 Parish Nov. 8, 193

FGREIGNHPATENTS j Number Countryv y Date t 511,013 Germany A1930 515,595

Germany l f `1931 

